private boolean performDoctypeOk() {
   int index = fDocumentTypeCombo.getSelectionIndex();
   if (index > -1) {
     String id = (String) fDocumentTypeIds.get(index);
     if (id == null || id.equalsIgnoreCase(SELECT_NONE)) {
       // if none, use null
       id = null;
     }
     try {
       HTMLContentProperties.setProperty(HTMLContentProperties.DOCUMENT_TYPE, getResource(), id);
     } catch (CoreException e) {
       // maybe in future, let user know there was a problem saving
       // file
       Logger.log(Logger.WARNING_DEBUG, e.getMessage(), e);
       return false;
     }
   }
   return true;
 }